Field of the Invention
The invention relates an encoder including a detecting function of an origin position.
Description of the Related Art
An encoder is currently used as a means for detecting a position and a velocity. An example of the encoder is an incremental encoder. Though a detecting position of the incremental encoder is accumulated by a counter when a scale and a sensor are relatively displaced, the detecting position is lost because the counter is reset just after supplying power. Thus, an operation for detecting an origin position is performed by relative displacement between the scale and the sensor when the power is supplied, and the counter is reset when the origin position is realized by an origin signal. This is origin detection. After origin detection, position detection from the origin position becomes performable.
In Japanese Patent Laid-Open No. 2013-36945, a photodiode array identical to a photodiode array of a displacement detecting sensor is used as an origin detecting sensor, and a plurality of patterns for generating an origin signal, which have the same pitch as a pattern for generating a displacement detecting signal, are used as a scale pattern. And when an origin signal processor processes an output signal acquired from them, an origin region is determined and an origin signal is output.
However, in Japanese Patent Laid-Open No. 2013-36945, if the photodiode arrays of the origin detecting sensor are arranged larger than a length corresponding to 2 periods of an output signal of the origin detection sensor, the origin region may be mistaken. Because an output signal in a region other than the origin region can be partially satisfied with a condition regarded as an origin by the origin signal processor.
In encoder disclosed in Japanese Patent Laid-Open No. 2012-103230, a digital origin signal is output based on an origin detecting signal reflected by a pattern for generating an origin signal and acquired by binarizing an output signal, which changes at a predetermined gradient and are entered into a detector.
However, in Japanese Patent Laid-Open No. 2012-103230, when the origin detecting signal varies on a high voltage side or a low voltage side by a noise, an output phase from a binarizing circuit changes and an origin position may be mistaken.